Since 2002 the United States has maintained a military detention facility at Guantánamo Bay, Cuba. Detainees from around the world are brought there as "enemy combatants." Some have been released. Detainees have the right, per ruling of the US Supreme Court, to challenge their detentions in federal court.
President Obama pledged during his 2008 campaign to close Guantánamo, but that has not happened yet. Where to send detainees who will not be tried but whom the government says cannot be released remains an obstacle. Where and how to prosecute the suspected enemy combatants is another. Congress will not allow Guantánamo detainees to be transferred and held in the US, unless they are awaiting trial.